Cardioprotective effect of adenosine in ischemia and reperfusion injury

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We have reported that ischemic preconditioning may limit infarct size by increasing 5'-nucleotidase activity. We tested whether alpha1-adrenoceptor stimulation in ischemic preconditioning mediates the infarct size -limiting effect through augmentation of 5'-nucleotidase activity. The coronary artery was occluded four times for 5 min separated by 5 min of reperfusion (ischemic preconditioning) in 82 dogs. Then the coronary artery was occluded for 90 min followed by 6 h of reperfusion. Infarct size normalized by risk area was smaller after ischemic preconditioning that in the control group, even though no difference existed in endomyocardial collateral flow during ischemic. Ectosolic 5'-nucleotidase activity was increased after ischemic preconditioning. However, prazosin blunted the infarct size-limiting effect of ischemic preconditioning. Intermittent alpha1-adrenoceptor stimulation by methoxamine mimicked the increase in 5'-nucleotidase activity and the infarct size-limiting effect, which were abolished by alpha, beta, -methyleneadenosine 5'-diphosphate. Identical results were obtained in the conscious model. Therefore, we conclude that increases in ectosolic 5'-nucleotidase activity due to alpha1-adrenoceptor activation may contribute to the infarct size-limiting effect of ischemic preconditioning.